Ingemar: I very much like that idea. Unfortunately I made an attempt to get this working but it is an utter failure in many senses... See below:

I figured this might be easy so I wrote this up real quick: http://dl.dropbox.com/u/4853895/WaterSimF2.zip

Its my WaterSimF2 unit I had a crack at and a TestApp using prometheus for drawing the TMX background and updating the water etc... It behaves a bit like water with one exception: IN REVERSE!!! Oo I have o idea why but it does XD

So if anyone wants a fluid system that works in reverse until all the water is gone or just wants to mess around with it, see the link above

Edit:
Screenie:

http://dl.dropbox.com/u/4853895/WaterSimF2_Screenie.png